Active SCR Performance
Indicates a problem with the Selective Catalytic Reduction (SCR) system performance.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
Your truck's computer is saying the SCR system isn't doing its job correctly, which is crucial for reducing harmful emissions from diesel engines.
What the computer is actually seeing
The computer monitors the efficiency of the SCR system by comparing the NOx levels before and after the catalyst. If the reduction is below a certain level, like less than 90% efficiency in reducing NOx, it triggers this code.
What a healthy reading looks like
NOx conversion efficiency should be above 90% under normal operating conditions. Monitor temperatures of both upstream and downstream NOx sensors; they should typically be around 300-500°F during operation.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check DEF tank level; it should be above 1/4 full. If low, fill it and clear the code. Decision point: Did the code return? Yes: go to step 2. No: end diagnosis.
- 22. Inspect wiring and connectors for the NOx sensors and SCR unit. Look for signs of damage or corrosion. Decision point: Is the wiring intact? Yes: go to step 3. No: repair or replace as necessary.
- 33. Test NOx sensors with a scan tool; compare readings against expected values. Decision point: Are the sensor readings within range? Yes: go to step 4. No: replace the faulty sensor.
- 44. Check for exhaust restrictions (dents, blockages) and inspect the SCR system for any leaks or physical damage. Decision point: Is the SCR system intact? Yes: go to step 5. No: repair or replace the damaged components.
- 55. Confirm SCR catalyst performance using a diagnostic tool, looking for efficiency ratings. Decision point: Is efficiency above 90%? Yes: you may have no fault. No: replace the SCR catalyst.
Common causes
- Faulty SCR catalyst
- Defective NOx sensors (upstream or downstream)
- Issues with the DEF system (low fluid, pump failure)
- Electrical connection issues
- Blocked or damaged exhaust system
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's not recommended to drive long distances or under heavy loads until the issue is resolved due to potential emissions system damage.
Will this code come back after clearing it?
If the underlying issue isn't fixed, this code will likely reappear after a few driving cycles.
Why does this code pair with other SCR codes?
These codes relate to different aspects of the SCR system; if one part isn't functioning, others may also fail.
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